Snapshot A 31-year-old woman with a medical history of schizophrenia is brought to the emergency department by her husband due to agitation, confusion, and delirium. Her temperature is 104°F (40°C), blood pressure is 162/108 mmHg, pulse is 110/min, and respirations are 31/min. On physical examination, she is diaphoretic, with generalized muscular rigidity. Laboratory testing is significant for a creatine kinase level of 4,680 IU/L. Her antipsychotic is removed, and supportive care is initiated. She is started on dantrolene for management of neuroleptic malignant syndrome. Introduction Mechanism of action blocks ryanodine receptors decreases excitation-contraction coupling decreases Ca2+ release from the sarcoplasmic reticulum in skeletal muscle Clinical use malignant hyperthermia hypermetabolic crisis secondary to inhaled anesthetic use (e.g., halothane) or succinylcholine patients have a genetic abnormality in ryanodine or dihydropyridine receptors, a skeletal muscle protein results in excessive Ca2+ release from the sarcoplasmic reticulum neuroleptic malignant syndrome (NMS) medical emergency secondary to neuroleptic use (e.g., antipsychotics) characterized by hyperthermia mental status change rigidity autonomic dysfunction